The invention relates to a fastening support.
Fastening supports of this kind are used to support machinery of the most diverse kind, and in particular, as regards automotive engineering, to support the power units.
Contrary to the case of a more complex support or bearing composed of several parts and equipped with a bearing spring usually of annular shape and of an intermediate support coupled to a separate shock absorber, a fastening support typically consists of an elastomer spring which herein preferably shall be integral and of two connection fittings, namely a first connection fitting acting as a support connection fitting and a second connection fitting acting as a load connection fitting to connect to the load. In general the elastomer spring is in the form of a body of rotation with its end faces in the radial plane. An annular channel is present approximately centrally between the two end faces and, following affixation of the elastomer spring in a hookup aperture present in the first connection fitting, it will be entered snugly, and optionally with slight prestressing, by the inside edge of the affixation aperture of the connection fitting. In general the spring comprises a continuous central borehole which in turn is fitted with a central sleeve passing a screw bolt. The sleeve is axially shorter than the relaxed spring, whereas the screw bolt is longer than the sleeve and furthermore may already project out of the relaxed spring. Load-receiving elements, foremost steel disks, are mounted on at least one, as a rule on the two mutually opposite end faces of the elastomer spring. The elastomer may be firmly connected in the manner of a rubber-metal compound to the connection fittings and also the connection fittings may be guided through the central screw bolt to loosely rest on the end faces of the elastomer spring. By screwing nuts on one or both sides of the screw bolt, the end-face connection fittings can be firmly pressed against the end-face edge of the central sleeve. As a result the elastomer spring of the fastening support will be prestressed. The particular degree of prestressing can be arbitrarily preselected as a function of the axial length of the sleeve. At the affixation side, the known, state-of-the-art elastomer spring used in the fastening supports and discussed here is configured in such manner that the elastomer spring can be xe2x80x9cforced-throughxe2x80x9d the aperture of the first connection fitting which usually is designed as a rest, tang or flange, with minimal deformation and stressing of this elastomer spring. For that purpose the elastomer spring is hooked up.
Such a presently conventional elastomer spring is shown in FIG. 1, FIG. 2 showing this spring assembled to a fastening support and in its prestressed but unloaded state. The references 1 denote the elastomer spring, 1.1 the segment of this spring acting as a shock absorber when compressed against the connection fitting 4.1, whereas, in the case of tensionxe2x80x94after shunting the applied force through the sleeve 3xe2x80x94the opposite connection fitting 4.2 on the other end face of the elastomer spring, the also compressed part 1.2 of the elastomer spring 1 being buffers to absorb the applied tension, and, in this example of the state of the art, the connection fitting 2, act as supports for the compressive and thrust forces applied to the elastomer spring. Furthermore radial guidance is implemented in the known fastening support by means of the approximately cylindrical elastomer segment 1.3 between the central sleeve 3 and the edge of the aperture in the connection fitting 2.
The drawback of the above described embodiment of a fastening support known already for many decades in innumerable variations is that the geometry of the elastomer spring is predicated on favorable fastening conditions and optimal elastomer protection during affixation. However such a geometry is a tradeoff against the service life of such typically dynamically loaded fastening supports because the forces introduced through the connection fittings 4.1 and 4.2 on one hand and through the connection fitting 2 acting as a support on the other hand, into the elastomer spring, will be applied at unequal radii. As a result considerable shearing forces are generated in the buffer segments 1.1 and 1.2 of the elastomer spring, entailing a degradation in the life of the bearings. It is known that buffers subjected solely to compression will allow higher loading, sometimes by an order of magnitude, than an identical elastomer spring undergoing thrust or shear stresses. In practice the solution to this conundrum to-date has been to use rubber grades offering excellent strengths. Recently however, and in particular as regards power-unit bearing in the automotive industry in the form of fastening supports of the kind being discussed herein, ever higher thermal resistance has been demanded, for which, while the elastomer grades indeed are available, on the other hand they permit only reduced dynamical loading relative to the previously used elastomer grades for fastening supports. Vice-versa, the rubber grades used heretofore lack the thermal resistance required by the automotive manufacturers.
Based on this state of the art, the objective of the invention is to so improve a fastening support of the initially described species that the elastomer spring offers longer service life, especially under dynamical loading, whereby dynamical-loading also will allow such service lives, with elastomer grades of lower strengths but higher thermal resistances, that correspond to the previously feasible service lives or are even superior to them.
The basic concept of the invention allowing the desired improvements therefore is to stress easy hookup of the elastomer spring into the connection fitting eye when configuring an integral elastomer spring for a fastening support, furthermore to pay equal attention in the geometric design of the elastomer spring to control beforehand the occurrence of the various stresses and to change them in order that foremost practically no shear stresses and hardly any thrust stresses shall arise in the elastomer spring. It is possible thereby to improve the service lives of the fastening supports of the invention under steady-state dynamic loading by a factor of 10 to 20 over the state of the art shown in FIGS. 1 and 2 while using identical elastomer mixtures. This feature in turn allowsxe2x80x94where required by the particular application(s)xe2x80x94to use elastomers, for instance EPDM which are mechanically more susceptible than many other elastomer mixtures but on the other hand are substantially more heat-resistant. Therefore the invention also allows manufacturing fastening supports having at least equal dynamic service lives and being optionally improved ones, that will concurrently withstand substantially higher operational temperatures. This feature is advantageous in automotive production, especially as regards motor vehicles, where fastening supports frequently are used as bearings for the drive units and where the higher performance requirements set on engines entailed steadily rising operational temperatures in recent years.
The basic concept to practically implement these insights assumes that the force-transmitting surfaces introducing loading and reaction forces into the elastomer spring must be set at equal radii relative to the direction of the load vector oriented axially parallel to the axis of rotation of the elastomer spring. This design is implemented primarily by a corresponding geometry of the elastomer spring and in subsidiary manner by a matching configuration of the hookup aperture.
Compared with the initially cited state of the art, this circumstance leads to the discovery that the radii of force introduction of the end-face circular force-flow surfaces of the integral elastomer fastening bodies must be enlarged and that the radii of force introduction of the flange-side rest surfaces must be decreased, and that simultaneously the effective areas of the force introducing surfaces, especially of the rest surfaces, be enlarged.
Especially good global-behavior bearing characteristics will be achieved when the axial bearing function and the radial stabilization of the bearing are transferred to mutually decoupled zones of the bearing""s elastomer spring. In a preferred embodiment of the invention, this feature is attained in that the radially inward zone and the cylindrical zone of the elastomer spring resting against the bearing""s sleeve are spaced apart by one or more notches or by at least one annular channel of cylindrical contour running coaxially with the fastening-support axis from the compressing cylinder, and by means of axially shortening at least the load connection fitting.
Decoupling the axial and radial functions in the bearing elastomer body furthermore is supported and enhanced in that the fastening-side end-face of the elastomer block is designed as an annular lip in the form of an umbrella or mushroom top, which opens toward the load side. Always with respect to the radial plane of the rotationally symmetrical integral elastomer spring, the outer conical angle a (FIG. 3) preferably shall be smaller than the inner conical angle xcex2 (FIG. 3), whereby the axial thickness of the annular bush is larger radially outward than inward. As a consequence, when the support has been assembled, the axial load on the annular lip will be predominantly radially outward, and the radially inward cylindrical segment of the elastomer spring near the sleeve,xe2x80x94used to radially stabilize the bearingxe2x80x94is practically decoupled in thrust-free manner, that is, it is insulated against vibrations, from the zones of the elastomer spring absorbing the axial compressive forces.
In the process, the thrust-free stress-decoupling of the radial stabilizing segments of the elastomer spring from the zones absorbing the axially directed compressions can be improved further in that an annular recess is present, which radially directly abuts the outer wall of the support sleeve, in the surface of the elastomer spring opposite the load side, and which acts to absorb any deformations occurring for instance in the radial support zone.
In order to control the elastomer spring deformations in the spring zones absorbing the axial stresses, particular or all connection fittings connected in force-transmitting manner with the elastomer spring must be configured in such manner by means of notched edges or shallow hollows to permit for instance curving, to preclude, by their being reversed, the evolution of the stresses. Such a system allows very accurate and fine tuning of the fastening support characteristics.
Preferably annular notches or deeper annular channels, the latter running axially, are formed in the zone of the intersections, located in the radial plane, of the various axial and radial surfaces constituting the seating zone for the cylindrical inner wall of the support connection fitting, in order that, foremost at hookup, the high peak stresses arising in particular in the vicinity of these intersections shall be avoided. Preferably the axial height of the annular channel cut out of the elastomer spring body must be so chosen for the purpose of seating the hookup flange that this height is equal to or only slightly less than the axial height of the hookup aperture.